Cast article



Patented Sept. 23, 1941 CAST ARTICLE Russell Franks, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a. corporation of West Virginia No Drawing. Application June I, 1940,

Seth N0. 339,327

4 Claims.

The invention relates to steels of the austenitic chromium-nickel type and refers more particularly to cast articles composed of such steels.

Austenitic chromium-nickel steels containing about 20% to 30% chromium, to 25% nickel, and up to 1% carbon are widely used in the cast condition for high temperature service. For some conditions of service the cast steel used may contain other alloying elements in addition to chromium and nickel. Thus, where resistance to intergranular deterioration at carbide precipitation temperatures is necessary, the steels commonly contain columbium in a proportion of 4 to 12 times the carbon content, or titanium in a proportion of 2' to times the carbon content, and where increased strength at elevated temperatures or increased resistance to specific corrodants is desired, the steels may contain 0.5% to 3.5% molybdenum. Manganese is often added in a proportion up to about 1%, and also nitrogen, to improve the quality of the steels.

As-cast steels of the composition described, are well suited in most respects to their use in high temperature service. They are resistant to many corrosive media and are adequately strong at moderately low temperatures. However, their ductility is poor at high temperatures between about 500 C. and 900 C. A cast tube or other vessel may to all outward appearances be in perfect condition yet fail suddenly without warning. The failure is not preceded by bulging or elongation such as usually precedes failure of ductile materials under stress.

This tendency of the cast chromium-nickel steels to fail at high temperature without warning is a disadvantage. While the length of life of articles composed of such steels may be entirely satisfactory, sudden failure of a part of an apparatus is dangerous to health and property. As a result, prudence requires frequent inspection and replacement long before the full life of the cast steel has been utilized.

It is a principal object of this invention to improve the ductility of cast austenitic chromium-nickel steels at high temperatures and thereby to prevent sudden, unexpected failure of such articles during use. This object is achieved by the addition of 1% to 6% manganese.

The invention accordingly comprises a cast article composed of austenitic chromium-nickel steel containing between and chromium, 5% to 25% nickel, 0.15% to 1% carbon, a substantial proportion not exceeding 5% of at least one ferrite-promoting element of the group consisting of titanium, columbium, and molybdenum, and 2% to 6% manganese, a proportion of manganese sufficient to impart to the steel improved ductility persisting at high temperatures. A preferred embodiment of the invention proportion of manganese is equally effective in a steel containing 25% chromium and 20% nickel.

The carbon content of steels to which manganese may be added to'secure the benefits of increased ductility should not exceed 1% and preferably should be less than 0.5%. Nitrogen in a proportion between 0.01% and 0.5% may be A substituted for part of thecarbon to improve the strength of the steel; the proportion of nitrogen is preferably between 0.1% and 0.3%.

Short time high temperature tensile tests on steels of various compositions illustrate the usefulness of the invention. In making these tests cast samples of the different steels, machined to standard (A. S. T. M.) 0.505 inch diameter tensile test specimens, were gradually brought to a temperature of 870 C. and held for approximately one-half hour at that temperature. The samples were then transferred to a standard tensile test machine equipped with a heated inufile for maintaining the sample at temperature throughout the test, and tensile stress was gradually applied until the sample failed. After each test the sample was removed from the testing machine and, allowed to cool to room temperature. The elongation and reduction of area of each sample were measured after cooling. Results of such tests are given in .the following table. T. S. means ultimate tensile strength in pounds per square inch, Per cent El means percentage elongation in two inches, and Per cent R. A. means reduction in area.

Tests at 870C. on cast Cr-Ni steels Analysis (rest Fe) Tensile test results Steel Per- Per- Per- Per- Per- Percent cent cent cent T. S. cent cent Cr Ni 0 Mn El R. A.

1 Contains 0.2 per cent nitrogen.

From the above table it is evident that the presence of manganese in cast chromium-nickel steeis'inoteriauy benefits the ductility of such steels at elevated temperature.

also ofbenefit in austenitic'chromium-nickel steels containing 10% to 20% chromium, 5% to 15% nickel, a substantial proportion not exceed-' 5% of at least one ferrite-promoting element of the group consisting of titanium, columbium, a d molybdenum, and 0.01% to 1% carbon. P eierably, the carbon is below 0.3%; a part of I claim:

1. A cast article for use at elevated temperatures and composed of an austenitic chromiumnickel steel containing 20% to 30% chromium; 5% to 25% nickel; a substantial proportion not exceeding 5% of at least one ierrite-promoting element of the group consisting of titanium, columbium, and molybdenum; carbon in a proportion between 0.01% and 0.5%; 0.01% to 0.5%

th'e carbon may be replaced by about 0.01% to 0.2% nitrogen. In steels containing 10% to 20%] chromium the proportion of manganese which is of greatest benefit is between 1% and 4%, the optimum being about 2%.

. Short timehigh temperature tensiletests made in the way explained above on representative chromium-nickel steels containing about 18% chromium and 8% to 10% nickel, and varying proportions. of manganese illustrate the bane-- ficial efi'ects of manganese on ductility'at high temperatures. Results of tests are given in the following table:

Tests at 870 C. on cast Cr-Ni steels Analysis (rest Fe) Tensile test results steel Per- Per- Per- Per- Per- Per- Percent cent cent cent cant .'I. 8. cent cent Cr. Ni 0 Ch Mn El R. A.

'11 18. 16 9.03 0.10 None 0. 49 17, 000 21 41 12 18. 04 0. 0. 10 None 0. 98 17, 000 25 40 13 18. 05 8. 65 0. 08 None 1. 60 14, 550 39 72 14 18. 15 10. 05 0. 06 0.75 0. 64 16, 625 25 61 15 18.87 10. 36 0. 07 0. 78 1. 65 17, 325 38 68 16 18. 02 10. 01 0. 08 0. 65 3. (B 19, 000 43 60 While specific examples have been given of such examples.

nitrogen;-and a proportion of manganese between 2% and 6%, efiective to impart enhanced ductility at elevated temperatures to the article; remainder iron. Y 2. A cast article for use at elevated temperatures between about 500 C. and 900 C. and com! posed of w an austenitic chromium-nickel steelcontaining 20% to chromium; 5% to 25% nickel; 0.5% to 3.5% molybdenum; carbon in a proportion between 0.15% and 0.5 0.01%lto 0.3% nitrogen; a proportion of manganese between 2%and 6%, 'efiective to impart enhanced ductility at elevat ed"temperatures 'to the article; remainder iron. 3. A cast article for use at elevated tempera- 3 tures and composed of an austenitic chromium-.

nickel steel containing 10% ,to 20% chromium;

3 exceeding 5% of at least one of the ferrite-' promoting elements titanium, columbium, and molybdenum; carbon ina proportion between 0.01%and 0.3%; 0.01% to 0.2% nitrogen; a proportion of manganese between 1% and 4%, efiective to enhance the ductility of such article at elevated temperatures; remainder iron.

4. A cast article for use at elevated temperatures between about 500 C. and 900 C. and composed. of an austenitic chromium-nickel steel containing 10% to 20% chromium; 5% to 15% nickel; 0.5% to 3.5% molybdenum; carbon'in a proportion between 0.01% and 0.3%; 0.01% to. 0.2% nitrogen; a proportion of manganese between 2% and 4%, eifective to impart enhanced ductility at elevated temperatures to the article; remainder iron.

- RUSSELL FRANKS. 

